1. Field of the Invention
The present invention relates to a coding and decoding apparatus of graphic animation data, and more particularly, to a coding and decoding apparatus of key information corresponding to time variables among the graphic animation data, and a method thereof.
2. Description of the Related Art
Graphic animation represents shape and attributes information of a 2-dimensional or 3-dimensiontal object, and expresses information on change and motion of the shape or attributes of each object with respect to time in a variety of ways. As a leading representation method for computer animation of an object on a time axis, there is a virtual reality markup language (VRML). This animation method is a key framing method for a 3-dimensional object, wherein a predetermined key frame is set on an arbitrary time axis, computer animation between respective set key frames is expressed by linear interpolation. The key frame used in this method is defined by an interpolator node, which consists of key data indicating key frame's location on the time axis and a key value data indicating the attributes of the key frame and motion information. That is, the key represents a time for expressing computer animation as a discontinuous value between 0 and 1, and the key value represents the attribute and location value of an object in a synthesized image at a time indicated by each key. FIG. 1 is a graph showing an example of the correlation between a key and a key value.
Meanwhile, when smooth computer animation similar to actual moving body is expressed according to the key framing method having the characteristic of a piecewise linear interpolation, a large amount of key frame information should be provided through interpolate nodes, and this causes a serious demerit in cost and efficiency when the method is used in application fields. That is, in off-line applications, a storage apparatus with a large capacity for storing a large amount of 3-dimensional animation data is needed. Also, in on-line applications, in addition to the problem in the off-line applications, high capacity and high speed of transmission channels for transmitting 3-dimensional animation data from a server to user terminals are needed. At the same time, due to increases in possible transmission errors, reliability of data is degraded. Accordingly, effective compression and coding function which can reduce the amount of node data is needed.
FIG. 2 is a schematic block diagram of the prior art coding and decoding apparatus.
Referring to FIG. 2, in the prior art, a method coding animation data using differential pulse code modulation (DPCM) is generally used. The characteristic of the key framing animation matches well with the DPCM method, and the method is appropriate to compress data. Also, the method using DPCM is used as an MPEG-4 binary format for scene (BIFS) coding method.
As shown in FIG. 2, a method for coding key data in an MPEG-4 BIFS coding method uses a first order DPCM in which DPCM processing is performed only once. In FIG. 2, a quantizer 105 quantizes key data K of an interpolator node to be coded. A DPCM processing unit 110 generates a differential value EK between neighboring data on a time axis in the quantized key data QK. The DPCM processed key data is input to an entropy encoder 115, and a compressed binary bit stream 120 is generated. The compressed binary bit stream 120 generated in an encoder 100 is generated as a restored key data item K^ through a decoder 150 which is constructed as an inverse process of the encoder 100. That is, the compressed binary bit stream 120 is restored to key data K^ through an entropy decoder 155, an inverse DPCM 160, and an inverse quantizer 165.
FIG. 3 is a detailed diagram of a DPCM shown in FIG. 2, and FIG. 4 is a detailed diagram of an inverse DPCM shown in FIG. 2.
Meanwhile, in order to increase the efficiency of coding in the entropy encoder 115, it is preferable that redundancy of data to be encoded, that is, data EK output from the DPCM processing unit 110 is high. However, if only the first order DPCM is performed for all as shown in FIG. 2, the effect of compression is not so high for data other than those data for which encoding through the first DPCM is appropriate.